1. Field of the Invention
Positioners may be linear or rotary, depending on whether they push-pull or turn. My invention is the rotary type; a shaft is turned through predetermined angles from a rest position. An example of its use is in the type of optical scanner in which a laser beam is reflected from a mirror attached to the side of the shaft (also called the armature), the location of the reflected spot being determined by the angle of the mirror/shaft assembly. The function of the positioner is to place the spot (the reflected beam), in a cyclical manner at a succession of places on the workpiece. Normally a positioner is not used to perform work, to slide or torque a workpiece--devices intended to do that operation must take account of the forces necessary to move the workpiece and are called actuators.
2. Description of Prior Art
The prior art consists of a magnetic field applied through conventional windings and pole pieces to a rotor, normally suspended on bearings and having a zero-current position dictated by a torsion element coaxial with the rotatable pole elements. The torque applied due to the magnetic field is resisted by the torsion element, usually a tiny shaft which is anchored at the outer end (or ends) and twists through a predictable angle, the angle being proportional to the applied torque due to the magnetic field which in turn is approximately proportional to the current in the windings. Galvanometers may have the windings in the stator or the armature (rotor). Galvanometers are rugged, fairly expensive to construct, and difficult to damp. They tend to oscillate about their final position until friction dissipates the rotary kinetic energy with which torque equilibrium was approached, and mechanical torque damping is difficult to obtain without introducing break-away static torque which impairs accuracy and sensitivity unduly.